Extremophiles
are microbes that live in conditions that would kill other creatures.
It was not until the 1970's that such creatures were recognized,
but the more researchers look, the more they discover that most
archaea, some bacteria
and a few protists
can survive in the harshest and strangest of environments.

addition,
the research into extremophile microbes has led to the confirmation
that the new domain of living organisms - the archaea
exists. Archaea are not the only extremophiles,
there are some eukaryotes
that live in such conditions.

Extremophiles
show how flexible life can be regarding its needs and its habitats.
Some of these microbes, particularly some bacteria and archaea,
also appear very simple in their composition.

Would
it be possible to create one of these microbes in the Laboratory?

Go
to Making Life?

Ice
lovers

Most space environments are cold and NASA researchers
are particularly interested in microbes that can survive at low
temperatures. Recently interest has focused on Lake
Vostok in Antarctica. NASA has had a research
expedition working at the lake throughout 1998 and 1999.

Lake Vostok is a huge freshwater lake which has
been frozen for perhaps a million years. Ice samples have
been retrieved from depths of nearly 4000m (1200 feet), and a
diverse assortment of bacterial species has been recovered.
At these depths the microbes have been cut off from sunlight and
other energy sources for a considerable time and are in a dormant
state, but still metabolizing at a very low-level of activity.
These findings are a good sign for the possibility of life being
able to survive on Europa, the ice-bound moon of Jupiter.

When water freezes, the life can go into suspension
and remain that way almost indefinitely until temperatures increase
to a level where activity can resume - ie liquid water.

In 1998, Richard
Hoover of NASA's Marshall Space Sciences Laboratory and Dr
S S Abyzov of the Russian Academy of Sciences found ice cores
from Lake Vostok contained microbes like one (above) which
is yet to be identified. Other life forms recovered from
the lake ice at depths as much as 3.5 km (about 2 miles) down
have been more recognizable and include cyanobacteria, bacteria,
fungi, spores, pollen grains, and diatoms. These organisms
are thought to have become trapped in the ice about 400,000 years
ago.

When
water freezes, the life can go into suspension and remain that way
almost indefinitely until temperatures increase to a level where
activity can resume - ie liquid water.

In
1998, Richard
Hoover of NASA's Marshall Space Sciences Laboratory and Dr S
S Abyzov of the Russian Academy of Sciences found ice cores from
Lake Vostock contained microbes like one (above) which is
yet to be identified. Other life forms recovered from the
lake ice at depths as much as 3.5 km (about 2 miles) down have been
more recognizable and include cyanobacteria, bacteria, fungi, spores,
pollen grains, and diatoms. These organisms are thought to
have become trapped in the ice about 400,000 years ago.

Acid
environments usually occur around active geothermal vents.
Though the immediate locality of such springs may be hot, the
temperature soon falls off outside the active areas. Many
of these hot springs are contaminated with sulfur, however, and
the water pH can be below five - acidic. Also acidity,
unlike heat, does not fall off outside the area of geological
activity. Other places where acidophiles occur include polluted
places, where industry or mining has left acidic waste.

Acidophiles,
however, cannot tolerate acid internally as this would break down
their cell structure, and they devote much effort to preventing
their environment from causing them damage. They produce
special enzymes for this task, and such enzymes have commercial
applications in many areas.

Alkaliphiles
live at the other extreme. Typical environments include
carbonate-rich soils and soda beds - the remnants of dried lakes.
These are found in dry climates such as the East African Rift
Valley and the Mojave Desert. As with acidophiles and for
the same reasons, alkaliphiles keep the alkali outside the cells
by the use of enzymes.

Another
group called halophiles,
live in salty environments. These are usually dried lake-beds
and salt-flats. Such environments can also become highly
alkaline, so the microbes that live there need to contend with
both high salt and alkalinity. The problem for salt-dwellers
is dehydration through osmosis and this is overcome by the organism
balancing the concentrations of solute inside and outside the
cell. Salts concentrate through lake evaporation, and such
lakes are common in hot dry regions of the world. Typical
air temperature conditions in salty lake beds are high,
frequently over 40 C (more than 100 F), with subsurface water
temperatures reaching as much as 65 C (150F). So the halophiles
are often thermophiles as well! Such lakes exist in California,
Israel (Dead Sea), Kenya, Australia and Mongolia.

Bacteria
and Archaea live in hot springs heated
by geothermal reactions deep in the Earth. Some springs reach
temperatures of 80 C (177F). The discovery of these heat-loving
bacteria is credited to Professor
Thomas D Brock, formerly of the University of Wisconsin at Madison.
The bacteria, Thermus aquaticus,
live in the hot springs of Yellowstone
National Park, Wyoming, and its discovery led to the development
of a highly useful bio-technology called Polymerase
Chain Reaction (PCR).
This is used for a wide variety of purposes including the production
of sugar from vegetable matter at high temperatures, in forensic
genetic fingerprinting, in medical diagnosis and in screening for
genetic and other diseases.

Professor
Brock's team also discovered organisms living in highly acidic
hot springs, Sulfolobus
acidocaldarius, and this
proved to be archaean. But the
most important conclusion that Professor Brock reached was that
life can exist anywhere that water remains liquid. This
assertion has far-reaching implications for the search for life
off planet Earth, and effectively lays the basic ground rules.

t
should be remembered that water boils at 100 C (212 F) only at
normal (standard) atmospheric pressure (one atmosphere).
If we increase the pressure, the boiling point temperature increases.
In the ocean on the mid-ocean ridges there are volcanic vents
that are constantly emitting hot water, gases and other materials
from deep inside the Earth. These vents are known as black
smokers and they are located on the sea floor, at depths of thousands
of feet. Here the pressures are many atmospheres - the pressure
underwater increases by one atmosphere for about every 10m (30
feet or so) depth. So down at such depths the pressure can
be 30 or more atmospheres and the boiling temperature very high.

Black
smokers (above left) can produce temperatures of 350 C
(662 F), but archaean microbes are still able to flourish, though
possibly not main-stream of the scalding flow. Nevertheless,
they are close to it and must be living at very high temperatures.
The water at this depth is still liquid and not superheated steam,
as it would be on the surface of the sea at this temperature.
One hyperthermophile that lives in this
environment is Methanopyrus,
which produces methane gas. It is important in the development
of life because it occupies a place at the bottom of the evolutionary
tree. So what does that tell us about early life on Earth
- was life a hyperthermophile extremophile? That seems likely,
as the Earth was a firey cauldron during its early history.

I

The
current record for temperature tolerance is held by Pyrodictium
Occultum, an archaean which
survived 121 C (250 F) for an hour. However, John Parkes
of Bristol University has evidence of microorganisms
living at 170 C (338 F) around volcanic vents on the ocean floor.

The
extremophiles that live around the mid-ocean ridges live at extreme
depths too, where the hydrostatic pressure is enormous.
But other organisms such as fish and crustaceans - lobsters -
live at these depths too. The secret is for the organism
to balance or equalize the internal and external pressures.

Holger
Jannasch leads a team of researchers at the Woods Hole Oceanographic
Institution in Massachusetts. Holger is one of the world's
leading experts on life around mid-ocean hydrothermal vents.
The Woods Hole team found Pyrolobus
fumarii, an Archaea, at the mid-Atlantic
ridge in 1996. Living at a depth of 3600 meters, and at
temperatures of up to 113 C (235 F) the microbe was able to survive
both in the presence of oxygen and without it. It is a chemoautotroph,
and survives with any intake of organic mater, on hydrogen, nitrates
and sulfates. It is one of best examples, so
far discovered, of a a microbe that can survive not just at one
extremes but in a variety of conditions. The researchers
claim that it is good evidence to reinforce the notion of life
living in the watery depths below the ice of Europa.

The
ocean floor, and specifically the mid-ocean ridges may be like
the Jupiter moon Europa.

Nanobacteria
have been found at extreme depths in the seabed sandstone off Western
Australia, as shown in this image (right). Again these
survive at extreme pressures.

There
is growing evidence that the ground beneath our feet is not just
home to a few odd archaea and bacteria, but is the habitat of trillions
of microbes. Additionally, it seems to have provided a comfortable
home for them for a long time - perhaps life even started in the
depths below. The evidence comes from analysis of minerals.
Some geologists, like Dr William A Fyfe of Ontario University,
believe that mineral concentrations could not possibly have been
created by geological processes. Instead, they now think that
such concentrations can only be made by biological processes as
a by-product of metabolism. Such minerals include gold
and other precious metals.

In
addition of course, we find oil and gas below the ground.
What role, if any, did subterranean archaea play in creating these?
Scientific opinion is changing from the accepted view that it is
the residue of surface life from millions of years ago, to one where
it is created by underground microbes. The idea was suggested
by Dr
Tom Gold, emeritus professor of astronomy at Cornell University,
in the nineteen-seventies but was not taken seriously until mounting
evidence came from other researchers. Dr
Henry L Ehrlich from Rensselaer Polytechnic Institute in Troy,
N Y, says that study is only just beginning.

Increasingly,
the evidence is mounting that the very rocks of the earth would
be totally different, chemically, without the intervention of life.
Recognizing this, planetary scientists now have an additional way
of assessing whether or not a planet is, or was, the habitat of
living organisms. This developing science will certainly be
applied to the analysis of Mars rocks and soil, when it becomes
available.

The
Mojave desert is one of the most inhospitable places on Earth.
Algae grow under white desert rocks,
where there is some moisture. The rocks have to be white
so that enough sunlight gets through to allow the algae to photosynthesize.
The Mojave lake-beds are a good place to look for Mars-like microbes.
There are lake-beds on Mars which may have life preserved in the
3.5 to 4 billion year old sediments left over from when the planet
had water. Unlike the Mojave, Mars will be extremely cold...

In
the Arctic
and Antarctic, life forms such as algae
and lichens cling on to their existence for prolonged periods
of time, waiting for the odd occasion when the temperature will
be high enough to allow ice to turn to water. Conditions
on Mars will be like this, but the likelihood of liquid water
occurring is remote now, though it certainly did exist in the
past.

Amber
is fossilized tree resin and it can preserve
creatures trapped in it for millions of years. Bacteria
were found to inhabit the gut of a bee trapped in amber and
where revived after a 25 million-year hibernation according to
researcher, by microbiologist Raul
Cano and Monica Borucki of California Polytechnic State
University. In 1995 the team announced they had revived
bacterial spores from the bee. This ancient bacterium, they
claimed, is genetically similar to Bacillus
sphaericus, which is a modern strain.
Interestingly, when subjected to adverse conditions they can go
into a form of suspended animation. They stop moving
and reproducing. They do without air and water. Their
metabolism virtually ceases.

The
Most Remarkable Microbe

Another
bacterium that has even more remarkable properties is Deinococcus
radiodurans. This includes being able to withstand
high levels of radiation that would kill other living entities,
including most bacteria. It can be classed as a polyextremophile.